1. Field of the Invention
The present invention relates to an LC high-pass filter circuit device, a laminated LC high-pass filter device, and a multiplexer which are suitable for use in, for example, a mobile communication device such as a cellular phone, and also relates to a radio communication apparatus.
2. Description of the Related Art
FIG. 16 shows the structure of a known laminated LC high-pass filter device of the type that is related to the present invention pertains. The known LC high-pass filter device, denoted generally by 151, has insulating sheets 152 to 158 which respectively support, as illustrated, input and output conductors 161 and 162, a resonance capacitive conductor 163, coiled conductors 164 to 169, and a grounding conductor 170.
The sheets 152 to 158 are stacked and baked to form an integral laminated structure 175 as shown in FIG. 17. An input terminal 176, an output terminal 177, and a grounding terminal G are formed on the laminated structure 175. The input conductor 161 is connected to the input terminal 176, and the output conductor 162 is connected to the output terminal 172. A grounding conductor 170 is connected to the grounding terminal G.
The coiled conductors 164 to 166 are connected in series through via holes 171b and 171c formed in the insulating sheets 155 and 156. Likewise, the coiled conductors 167 to 169 are connected in series through via holes 172b and 172c formed in the insulating sheets 155 and 156. The series connection of the coiled structures 164 to 165 defines an inductor L1, while the series connection of the coiled conductors 167 to 169 defines an inductor L2. The inductor L1 is electrically connected at one end thereof to the input conductor 161 through a via hole 171a formed in the insulating sheet 154. Similarly, the inductor L2 is electrically connected at one end thereof to the output conductor 162 through a via hole 172a formed in the insulating sheet 154. The other ends of the inductors L1 and L2 are electrically connected to the grounding conductor 170 through via holes 171d and 172d formed in the insulating sheet 157. The direction of winding of the inductor L1 and the direction of winding of the inductor L2 are opposite to each other. The capacitive conductor 163 opposes the input conductor 161 and the output conductor 162 across the insulating sheet 153 so as to define a resonance capacitor C.
FIG. 18 shows a circuit that is electrically equivalent to the laminated LC high-pass filter device 151 having the construction described above. Since the inductors L1 and L2 are wound in opposite directions, the inductors L1 and L2 are back-coupled to each other. Therefore, the -M produced by the inductive back-coupling of the inductors L1 and L2, the resonance capacitor C and the inductors L1 and L2 in combination define a trap circuit.
In the known LC high-pass filter 151 having the above-described construction, the major planes of the input conductor 161, output conductor 162 and the grounding conductor 170 substantially perpendicularly cross the lines of magnetic force generated by the inductors L1 and L2, due to the fact that the inductors L1 and L2 are respectively defined by the coiled conductors 164 to 166 and coiled conductors 167 to 169. Consequently, the lines of magnetic force generated by the inductors L1 and L2 produce large eddy current loss in, for example, the grounding conductor 170. This leads to production of the LC high-pass filter device 151 having a small Q value. In addition, it has been difficult to reduce the size, in particular the planar area, of the LC high-pass filter device 151, because the coiled conductors 164 to 166 and the coiled conductors 167 to 169 occupy considerably large areas.
In addition, with the equivalent circuit shown in FIG. 18, it is difficult to implement a high-pass filter device in which the attenuation pole of the trap circuit is positioned near the central frequency of the high-pass filter circuit.
In order to overcome the problems described above, preferred embodiments of the present invention provide an LC high-pass filter circuit device which has a high Q value and excellent frequency characteristics, and a laminated LC high-pass filter device, a multiplexer and a radio communication apparatus which include such a novel LC high-pass filter circuit device.
According to a preferred embodiment of the present invention, a LC high-pass filter circuit device includes a pair of terminals including an input terminal and an output terminal, at least two high-pass filter circuits including first capacitors connected in series between the input and output terminals and first inductors connected to the input and output terminals in parallel with each other and grounded, each of the high-pass filter circuits having one first capacitor and one first inductor, and a trap circuit including a series connection of a second capacitor and a second inductor, the series connection being grounded at one end and connected between two adjacent high-pass filter circuits so as to shunt from the input and output terminals.
Preferably, the first capacitor of each high-pass filter circuit is connected between the associated first inductor and the trap circuit.
With these unique structural features and arrangement, it is possible to locate the attenuation pole of the trap circuit at a position near the pass band of the high-pass filter circuit and, therefore, to obtain an LC high-pass filter circuit device having a sharp frequency characteristic.
The LC high-pass filter circuit device may further include third capacitors connected between the terminals and the node between the second capacitor and the second inductor of the trap circuit, the third capacitors defining band-adjusting capacitors.
This arrangement permits a signal path of a low impedance to be formed separately. Lower impedance allows greater signal traffic, making it possible to widen the pass-band of the LC high-pass filter circuit device.
According to another preferred embodiment of the present invention, a laminated LC high-pass filter device includes a laminated structure including a stack of a plurality of insulating layers, a plurality of capacitive conductors, and a plurality of coiled conductors, an input terminal, an output terminal, and a grounding terminal provided on surfaces of the laminated structure, a plurality of high-pass filter circuits disposed in the laminated structure, each of the high-pass filter circuits having a first capacitor defined by one of the capacitive conductors and a first inductor defined by one of the coiled conductors, and a trap disposed in the laminated structure and having a series connection of a second capacitor and a second inductor, the second capacitor being defined by one of the capacitive conductors and the second inductor being defined by one of the coiled conductors, wherein the first capacitors of the high-pass filter circuits are connected in series between the input terminal and the output terminal, and the first inductors of the high-pass filter circuits are connected to the input terminal and the output terminal in parallel to each other and are connected also to the grounding terminal, and wherein the trap is connected between two adjacent high-pass filter circuits so as to shunt from the input terminal and the output terminal, the series connection of the second capacitor and the second inductor being connected to the grounding terminal.
The arrangement may be such that at least a portion of the coiled conductor constituting the first inductor and at least a portion of the coiled conductor constituting the second inductor are defined by inductor via holes formed in the insulating layer or, alternatively, by a helical coiled conductor or a spiral coiled conductor. Inductor via holes have axes extending in the direction of the stack of layers that defines the laminated structure. By forming at least a portion of the inductors by such inductor via holes, it is possible to obtain an LC high-pass filter or a trap having high Q value. In addition, the area of the LC high-pass filter can be reduced because the inductor via holes occupy only small areas.
The arrangement also may be such that the coiled conductor constituting the first inductor and the coiled conductor constituting the second inductor are located at different positions in the stacking direction of the stacked layers forming the laminated structure. Thus, the first inductor and the second inductor provide a multi-stage arrangement within the laminated structure. This arrangement minimizes the electromagnetic coupling between the LC high-pass filter having the first inductor and the trap having the second inductor, thus preventing degradation of the high-frequency characteristic, while reducing the planar area of the laminated LC high-pass filter device.
It is also preferred that the trap is disposed at a level or vertical position that is higher than that of the high-pass filter circuits in the stacking direction of the insulating layers. This arrangement prevents electric fields and magnetic fields from leaking to the exterior of the laminated LC high-pass filter device through the first inductors of the high-pass filter circuits.
The arrangement may also be such that the first inductor of each of the high-pass filter circuits has a major portion constituted by an inductor via hole having an axis extending in the stacking direction of the insulating layers and a minor portion constituted by a helical coiled conductor or a spiral coiled conductor provided on the surface of the insulating layer, the major and minor portions being electrically connected to each other. This arrangement advantageously reduces the height of the first inductors of the high-pass filter circuits.
According to other preferred embodiments of the present invention, a multiplexer and a radio communication apparatus each includes a laminated LC high-pass filter device according to preferred embodiments described above. The multiplexer and the radio communication apparatus thus obtained have greatly reduced sizes.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the attached drawings.